Multicellular compositions of pluripotent human embryonic stem cells and cancer cells

ABSTRACT

Methods are provided for producing novel multicellular compositions comprising cancer cells together with pluripotent human stem cells, which are capable of proliferating and differentiating into various normal cell lines and tissue structures. These novel multicellular compositions are useful for investigating the properties of cancer cells in a normal human tissue microenvironment, and for studying interventions that will modulate these properties including devising, testing and screening therapeutic drugs.

FIELD OF THE INVENTION

The present invention relates to multicellular compositions comprisingcancer cells together with pluripotent human embryonic stem cells, inwhich the latter are capable of proliferating and differentiating intovarious normal cell lines. The invention further relates to methods ofproducing the multicellular compositions and to use of saidmulticellular compositions, inter alia in methods for drug screening andfor evaluating the efficacy of cancer therapy.

BACKGROUND OF THE INVENTION

There is at present no readily available experimental system in whichhuman cancer cells can be grown in the context of a mixed population ofnormal differentiated human cells. Such an experimental system would beadvantageous for investigating responses to anticancer therapies and forexploring biological aspects of cancer cell growth (e.g. tumor cellinvasion, angiogenesis, proliferation, migration and metastasis amongothers). Pluripotent human embryonic stem cells (hESC) are capable ofdifferentiating into many distinct normal cell types, which makes themand their derivatives suitable candidates for research and medicalapplications.

U.S. Pat. No. 5,690,926 discloses non-murine pluripotential cells,including human pluripotential cells, that have the ability to bepassaged in vitro for at least 20 passages and which differentiate inculture into a variety of tissues.

EP Patent No. 380646 discloses to the use of leukaemia inhibitory factor(LIF), in the isolation and propagation of embryonic stem cells invitro.

U.S. Pat. No. 5,453,357 discloses a non-mouse pluripotential embryonicstem cell which can: (a) be maintained on feeder layers for at least 20passages; and (b) give rise to embryoid bodies and multipledifferentiated cell phenotypes in monolayer culture. The inventionfurther provides a method of making a pluripotential embryonic stem cellcomprising administering a growth enhancing amount of basic fibroblastgrowth factor, leukemia inhibitory factor, membrane associated steelfactor, and soluble steel factor to primordial germ cells under cellgrowth conditions, thereby making a pluripotential embryonic stem cell.

U.S. Pat. No. 5,753,506 discloses a method of screening factors for theability to promote the formation of embryonic stem cells, comprisingcombining primordial germ cells with a factor selected from the groupconsisting of fibroblast growth factor, leukemia inhibitory factor,membrane associated steel factor, and soluble steel factor with thefactor to be screened and determining the formation of embryonic stemcells, whereas the formation of embryonic stem cells indicates a factorcapable of promoting the formation of embryonic stem cells.

A method of enriching a population of mammalian cells for stem cells isdisclosed in U.S. Pat. No. 6,146,888. The method comprises the steps of:providing in vitro a mixed population of mammalian cells whose genomecomprises at least one nucleic acid construct encoding an antibioticresistance gene operatively linked to a promoter which preferentiallyexpresses said antibiotic gene in mammalian stem cells.

A method for culturing human embryonic stem cells in vitro for prolongedmaintenance while preserving the pluripotent character of these cells,as well as a purified preparation of said cells, is disclosed in U.S.Pat. No. 6,200,806. It is further disclosed that these embryonic stemcells also retain the ability, throughout the culture and aftercontinuous culture for eleven months, to differentiate into all tissuesderived from all three embryonic germ layers.

A method for selective ex-vivo expansion of stem cells is disclosed inU.S. Pat. No. 6,479,261. The method comprises the steps of separatingstem cells from other cells and culturing the separated stem cells in agrowth media comprising a modified human interleukin-3 polypeptidehaving at least three times greater cell proliferative activity thannative human interleukin-3, in at least one assay selected from thegroup consisting of: AML cell proliferation, TF-1 cell proliferation andmethylcellulose assay.

A method of inducing angiogenesis in a tissue of a mammal, comprisingthe step of implanting a microorgan within the tissue of the mammal, isdisclosed in International Publication No. WO 01/00859. The microorganis derived from said mammal or from another mammal, wherein the organmay be selected from the group consisting of a lung, a liver, a kidney,a muscle, a spleen, a skin and a heart.

A genetically modified micro-organ explant expressing at least onerecombinant gene product and methods for generating thereof, wherein themicro-organ explant comprises a population of cells and maintains amicroarchitecture of an organ from which it is derived and at the sametime having dimensions selected so as to allow diffusion of adequatenutrients and gases to cells in the micro-organ explant is disclosed inInternational Publication No. WO 03/035851

A population of hESC which under appropriate culture conditionsdifferentiate into a substantially high percentage of insulin producingcells in spontaneously formed aggregated embryoid bodies is disclosed inInternational Publication No. WO02/092756 which is assigned to theapplicant of the present invention.

Partially committed progenitors derived from embryonic stem cells thatexpress telomerase and not being terminally differentiated and hence arecapable of continued proliferation, are disclosed in InternationalPublication No. WO 03/066839 which is assigned to the applicant of thepresent invention.

Nowhere in the background art is it taught or suggested that amulticellular compositions comprising human embryonic stem cells andcancer cells of human origin may be cocultured and moreover useful fordrug screening.

SUMMARY OF THE INVENTION

The present invention provides multicellular compositions comprisingpluripotent human embryonic stem cell together with human cancer cellswherein the stem cells maintain the ability to proliferate and todifferentiate partially or fully, thereby forming a microenvironment ofnormal human tissue; and the cancer cells maintain their abnormalphenotype. In particular, the present invention providesthree-dimensional structures comprising pluripotent human embryonic stemcells or differentiated cells derived from hESC in contact with humancancer cells. The cancer cells may be selected from established celllines and primary cell cultures. The pluripotent stem cells can formembryoid bodies into which human cancer cells are introduced. Typically,embryoid bodies may be maintained in culture, or may be introduced intoa suitable host animal. Within a suitable host animal embryoid bodiescan give rise to teratomas. Accordingly, the cancer cells may beintroduced either into the embryoid bodies or into the teratomas derivedthereform.

The present invention further provides methods for producing amulticellular composition comprising pluripotent stem cells and cancercells, wherein the stem cells maintain the ability to proliferate and todifferentiate partially or fully, thereby forming a microenvironment ofnormal human tissue; and the cancer cells maintain their abnormalphenotype.

The present invention further provides methods of screening therapeuticentities or modalities, including but not limited to anticancer drugs,immunotherapeutic drugs and agents for gene therapy, utilizingmulticellular compositions comprising pluripotent stem cells togetherwith cancer cells.

The present invention further provides methods for evaluating treatmentefficacy of therapeutic agents, including but not limited to anticancerdrugs, immunotherapeutic drugs and agents for gene therapy, utilizingmulticellular compositions comprising pluripotent stem cells togetherwith cancer cells.

The present invention is based in part on the unexpected finding thatcancer cells of human origin that are grown within a teratoma derivedfrom human embryonic stem cells, maintain their abnormal phenotype.

It is now disclosed for the first time that human cancer cells grown invivo within a normal human microenvironment derived from human embryonicstem cells implanted in immunodeficient mice, invade the normalmicroenvironment and furthermore induce angiogenic activity within thenormal human tissue. This induced angiogenic activity results in thegeneration of blood vessels of human origin.

According to one aspect, the present invention provides a multicellularcomposition comprising cancer cells within a microenvironment of normalhuman cells selected from the group consisting of: pluripotent humanembryonic stem cells and normal human tissue derived from differentiatedhuman embryonic stem cells; wherein the cancer cells maintain theirabnormal phenotype.

It should be recognized that the present invention providesmulticellular compositions, comprising human tumor cells growing withina human cellular microenvironment derived from differentiated humanembryonic stem cells, in vitro and in vivo. In vitro, the multicellularcomposition of the invention comprises at least one embryoid bodycomprising cancer cells. In vivo, the multicellular composition of theinvention comprises at least one teratoma comprising cancer cells.

According to one embodiment the present invention provides amulticellular composition comprising an embryoid body comprising humanembryonic stem cells together with human cancer cells. According toanother embodiment the present invention provides a multicellularcomposition comprising normal human tissue derived from differentiatedhuman embryonic stem cells and cancer cells.

According to one embodiment the multicellular compositions aremaintained in culture. According to another embodiment, themulticellular compositions are implanted within a host animal. Accordingto some embodiments the multicellular compositions are implantedintraperitoneally and maintained in ascites form. According to someembodiments the multicellular compositions are implanted into apredetermined site within the host animal and develop into teratomas.According to some embodiments the embryoid bodies are occluded withinbarrier membranes prior to implantation.

According to yet another embodiment the cancer cells of themulticellular composition of the present invention invade the normalhuman microenvironment derived from human embryonic stem cells.

According to yet another embodiment, the cancer cells induce angiogenicactivity in the normal human microenvironment derived from humanembryonic stem cells. According to yet another embodiment the cancercells elicit formation of new human blood vessels within the normalhuman microenvironment derived from human embryonic stem cells. Thehuman origin of the newly formed blood vessels may be verified usingcell surface markers as are well known in the art.

According to yet another embodiment at least some cells in themulticellular composition comprise a construct comprising at least oneexogenous polynucleotide. According to yet another embodiment, at leastsome cells in the multicellular composition comprise a vector comprisingat least one exogenous polynucleotide. According to yet anotherembodiment, the vector is a plasmid or a virus. According to yet anotherembodiment, the vector is a virus selected from the group consisting of:adenoviruses, retroviruses and lentiviruses.

According to yet another embodiment, the exogenous polynucleotide isstably integrated into the genome of said at least some cells. Accordingto yet another embodiment, the exogenous polynucleotide is transientlyexpressed by the at least some cells.

According to yet another embodiment, the construct further comprises atleast one regulatory element. According to yet another embodiment, theat least one regulatory element is selected from the group consistingof: promoter, enhancer, post transcriptional element, initiation codon,stop codon, polyadenylation signal and selection marker. According toyet another embodiment, the exogenous polynucleotide is operably linkedto expression control sequences.

According to yet another embodiment the cancer cells are transfectedwith a marker gene. According to yet another embodiment the cancer cellsare stably transfected with a marker gene. According to certainexemplary embodiments, the marker is selected from a group consistingof: nuclear histone H2A-green fluorescent fusion protein (HEY-OFP), redfluorescent protein (RFP) with nuclear localization signal (NLS).

According to another aspect the present invention relates to methods ofproducing multicellular compositions in vitro and in vivo comprisingnormal human cells derived from human embryonic stem cells together withcancer cells. The methods comprise culturing hESC in conditions suitablefor the formation of embryoid bodies or teratomas, which serve as anartificial microenvironment of normal human tissue for the cancer cells.

According to one embodiment the present invention provides a method forthe formation of multicellular compositions comprising cancer cells ofhuman origin within a normal human tissue derived from human embryonicstem cells, comprising:

-   -   (a) culturing hESC in conditions which promote formation of        embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body;        and    -   (d) determining the presence of cancer cells within said at        least one embryoid body.

According to another embodiment, the method further comprises:

-   -   (e) injecting said at least one embryoid body into a defined        locus in a host animal.

According to another embodiment, the method further comprises:

-   -   (f) determining the formation of at least one teratoma in the        locus of injection.

According to an alternative embodiment, step (e) comprises injectingsaid at least one embryoid body into the peritoneal cavity of a hostanimal.

According to an alternative embodiment, step (e) comprises injectingsaid at least one embryoid body into the host animal, wherein said atleast one embryoid body is occluded within a barrier membrane prior toimplantation.

According to yet another embodiment, the present invention provides amethod for the formation of multicellular compositions comprising cancercells of human origin within a normal human tissue derived from humanembryonic stem cells, in vivo, comprising:

-   -   (a) injecting undifferentiated human embryonic stem cells into a        host animal;    -   (b) determining the formation of at least one teratoma in the        locus of injection;    -   (c) injecting cancer cells into the at least one teratoma of        (b); and    -   (d) determining the presence of cancer cells within the at least        one teratoma.

According to yet another embodiment, the undifferentiated humanembryonic stem cells are injected into a defined locus in the hostanimal. According to yet another embodiment, the undifferentiated humanembryonic stem cells are injected into the peritoneal cavity of a hostanimal. According to yet another embodiment, the undifferentiated humanembryonic stem cells are occluded within a barrier membrane prior toimplantation in a host animal.

According to certain alternative embodiments, the cancer cells areestablished cell lines or primary tumor cells. Preferably, the cancercells are of a human origin. The cancer cells may be derived from solidmalignant tumors, non-solid malignant tumors, and hematologic cancers.According to particular embodiments of the present invention the cancercells may be selected from the group consisting of: prostate cancer,breast cancer, ovarian cancer, lung cancer, melanoma, renal cancer,bladder cancer, fibrosarcoma, hepatocellular carcinoma, osteocarcinoma,primary ductal carcinoma, giant cell sarcoma, ductal carcinoma,Hodgkin's disease, colorectal carcinoma, lymphoma, transitional cellcarcinoma, uterine sarcoma, adenocarcinoma, plasmacytoma, epidermoidcarcinoma, Burkitt's lymphoma, Ewing's sarcoma, gastric carcinoma,squamous cell carcinoma, neuroblastoma, rhabdomyosarcoma.

According to a yet another aspect, the present invention providesmethods of screening therapeutic agents using a multicellularcomposition comprising cancer cells of human origin and normal humantissue derived from human embryonic stem cells, the method comprisingcontacting the multicellular composition with at least one candidatetherapeutic agent, and determining its effect on the multicellularcomposition.

According to yet another embodiment, the present invention provides amethod for screening, in vitro, the effect of a therapeutic agent oncancer cells comprising:

-   -   (a) culturing human embryonic stem cells in conditions which        promote generation of embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body;    -   (d) determining the presence of cancer cells within said at        least one embryoid body;    -   (e) contacting said at least one embryoid body to a composition        comprising a therapeutic agent; and    -   (f) determining whether the therapeutic agent has an effect on        the at least one embryoid body.

According to yet another embodiment, determining the effect of thetherapeutic agent on the at least one embryoid body comprises evaluatingat least one of the following parameters: cell proliferation, celldifferentiation, invasiveness of the cancer cells, angiogenesis andapoptosis.

According to yet another embodiment, the therapeutic agent is selectedfrom the group consisting of: a cytotoxic compound, a cytostaticcompound, anticancer drug, an antisense compound, an anti-viral agent,an agent inhibitory of DNA synthesis and function and an antibody.

According to one embodiment, the present invention provides a method ofscreening therapeutic agents, in vivo, comprising:

-   -   (a) injecting undifferentiated human embryonic stem cells into a        host animal;    -   (b) determining the formation of at least one teratoma in the        host animal;    -   (c) injecting cancer cells into the at least one teratoma;    -   (d) determining the presence of cancer cells within said at        least one teratoma;    -   (e) treating the host animal having said at least one teratoma        with a composition comprising a candidate therapeutic agent; and    -   (f) determining whether the therapeutic agent has an effect on        said at least one teratoma.

According to an alternative embodiment, in step (a) the undifferentiatedhuman embryonic stem cells are injected into the peritoneal cavity of ahost animal.

According to yet another embodiment, treating the host animal isperformed by topical administration of said therapeutic agent to said atleast one teratoma.

According to certain alternative embodiment, the method comprises:

-   -   (a) culturing hESC in conditions which promote generation of        embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body        thereby obtaining at least one multicellular composition;    -   (d) determining the presence of cancer cells within the at least        one multicellular composition;    -   (e) injecting said at least one multicellular composition into a        host animal;    -   (f) treating the host animal having said at least one        multicellular composition with a therapeutic agent; and    -   (g) determining whether the therapeutic agent has an effect on        said at least one multicellular composition.

According to an alternative embodiment, the at least at least onemulticellular composition is injected into a site selected from adefined locus in said host animal and the peritoneal cavity of a hostanimal.

According to an alternative embodiment, step (e) comprises injectinginto the host animal said at least one at least one multicellularcomposition, wherein said at least one at least one multicellularcomposition is occluded within a barrier membrane.

According to an alternative embodiment, step (g) comprises determiningthe effect of said at least one therapeutic agent on the multicellularcomposition.

According to yet another embodiment, treating the host animal isperformed by intralesional administration of said therapeutic agent tothe multicellular composition.

According to yet another embodiment, the therapeutic agent is conjugatedto an agent selected from the group consisting of: imaging agent and acarrier.

According to yet another embodiment, the imaging agent is selected from,but not restricted to, paramagnetic particles: gadolinium, yttrium,lutetium and gallium; radioactive moieties: radioactive indium, rheniumand technetium; and dyes: fluorescin isothiocyanate (FITC), greenfluorescent protein (GFP), cyan fluorescent protein (CFP), rhodamine I,II, III and IV, rhodamine B, and rosamine.

According to yet another embodiment, the therapeutic agent is animmunotherapeutic agent of human origin, selected from the groupconsisting of: an antibody or active fragments thereof, a cytokine, achemokine, a polynucleotide encoding same and a cell of the immunesystem.

According to yet another embodiment, the therapeutic agent comprises atleast one oligonucleotide, selected from antisense, sense nucleotidesequence, short interfering RNA, ribozyme and aptamer.

According to yet another aspect, the present invention provides a methodfor evaluating treatment efficacy of therapeutic agents, including butnot limited to anticancer drugs, immunotherapeutic drugs and agents forgene therapy, utilizing multicellular compositions comprising normalhuman tissue together with cancer cells.

According to one embodiment, the present invention provides a method forevaluating treatment efficacy of therapeutic agents, comprisingcontacting a plurality of multicellular compositions with a therapeuticagent and assessing the damage caused by the therapeutic agent to thenormal human tissue.

According to another embodiment, the present invention provides a methodfor evaluating treatment efficacy of therapeutic agents, comprisingcontacting a plurality of multicellular compositions with a therapeuticagent and assessing the damage caused by the therapeutic agent to thecancer cells.

According to yet another embodiment, the damage caused by thetherapeutic agent is assessed by evaluating at least one of theparameters selected from the group consisting of: cell proliferation,cell differentiation, invasiveness of the cancer cells, angiogenesis andapoptosis.

According to yet another embodiment, the therapeutic agent is acytotoxic compound selected from, but not restricted to, agentsinhibitory of DNA synthesis and function selected from the groupconsisting of: adriamycin, bleomycin, chlorambucil, cisplatin,daunomycin, ifosfamide and melphalan; agents inhibitory of microtubule(mitotic spindle) formation and function: vinblastine, vincristine,vinorelbine, paclitaxel (taxol) and docetaxel; anti metabolites:cytarabine, fluorouracil, fluoroximidine, mercaptopurine, methotorexate,gemcitabin and thioquanine; alkylating agents: mechlorethamine,chlorambucil, cyclophosphamide, melphalan and methotrexate; antibiotics:bleomycin and mitomycin; nitrosoureas: carmustine (BCNU) and lomustine;inorganic ions: carboplatin, oxaloplatin; interferon and asparaginase;hormones: tamoxifen, leuprolide, daunomycin, flutamide and megestrolacetate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages willbecome apparent when reference is made to the following detaileddescription of the invention and the accompanying drawings in which:

FIG. 1 presents a schematic presentation of a representativeexperimental protocol for developing cancer cells in teratomas within ahost animal.

FIG. 2 is photomicrographs of teratoma, tumor and boundary region usingreticulin staining with Gomori technique showing: (A) Typical appearanceof teratoma derived structure in SCID/beige mice, with derivatives ofthree embryonic germ layers [se: stratified epithelium of ectodermalorigin, m: smooth muscle of mesodermal origin, ce: columnar epitheliumwith goblet cells of endodermal origin]; (B) Homogeneous mass of HEYovarian carcinoma tumor cells (tu); and (C) Boundary region of tumorcells (tu) adjacent to a differentiated teratoma structure consisting ofa neurovascular bundle with a venule (v) arteriole (a) and a nerve (n).Bar=200 μm in all three panels.

FIG. 3 shows infiltration of HEY-GFP cells into human teratoma derivedtissue: (A) arrows indicate HEY-GFP positive nuclear immunostaining ofHEY-GFP cells in a field of tumor cells (Bar=50 μm); and (B) and (C)arrows indicate migration of tumor (tu) derived GFP positive cells intothe teratoma (te) derived adipocytes (ad) and crossing adjacent nervetissue (n), (Bar=50 μm).

FIG. 4 exhibits detection of tumor neo-angiogenesis using human specificCD34 antibodies: (A) a specimen of human breast carcinoma stained withanti CD34 human specific antibody as a positive control (Bar=50 μm); (B)photomicrographs showing low power magnifications of CD34 positiveimmunostaining of an arteriole adjacent to a mass of HEY tumor cellsgrowing within a human teratoma (Bar=100 μm); (C) higher-powermagnification of the inset from B demonstrating specificity of stainingof the endothelial cell layer (Bar=20 μm); and (D-F) additional humanCD34 positively staining blood vessels adjacent to and within tumorcells [a: arteriole, v: venule, by: blood vessel, tu: tumor](Bar=50 μmfor panel D, Bar=100 μm for panel E and Bar=50 μm for panel F).

FIG. 5 presents photomicrographs of mouse-specific CD31 immunostaining:(A) normal mouse hepatic sinusoidal endothelium stained with anti-CD31mouse specific antibody as positive control [cv: central hepaticvein](Bar=50 μm); (B) mouse specific anti-CD31 immunostaining of bloodvessels in a tumor nodule following direct intramuscular injection(Bar=50 μm); and (C) absence of signal in mouse specific anti-CD31antibody stained section containing a neurovascular structure (Bar=50μm).

DETAILED DESCRIPTION OF THE INVENTION

It has long been appreciated that the stroma surrounding tumor isfrequently modified in terms of cellular composition and extracellularmatrix during the course of tumor growth. Furthermore, tumormicroenvironment has been shown to greatly influence tumorigenicityproperties both at the site of the primary tumor and at metastasticsites. Thus for example, it has been demonstrated that human prostaticcarcinoma-associated fibroblasts can promote carcinogenesis in humanprostate epithelial cells which have been initiated, but which are notyet tumorigenic (Olumi et al., Cancer Res. 52: 5002-5011, 1999).Conversely, in the case of ovarian cancer cell lines, it was shown thattumor growth induced by injection of these cell lines in nude mice couldbe reduced by co-injection of normal bovine or human ovarian stromalcells, but not by co-injection of other stromal cell types (Parrott etal., Mol. Cell. Endocrinol, 175: 29-39, 2001). Interestingly however,the normal ovarian stromal cells did not appear to survive long-termincubation at the tumor site, which was instead supported by therecruitment of host murine stromal cells. Normal keratinocytes have alsobeen shown to suppress early stages of neoplastic progression in skinepithelia (Javaherian et al., Cancer Res. 58:2200-2208, 1998).

The present invention provides an experimental platform for growth ofhuman tumor cells within a microenvironment of normal humandifferentiated cells. Experimental system in which human cancer cellscan be grown in the context of a mixed population of normaldifferentiated human cells may serve as an innovative platform fortesting biological aspects of cancer cell growth (e.g. tumor cellinvasion, angiogenesis) or response to anticancer therapies.

Numerous models have been previously developed for human tumorigenesis,for studying properties of tumor cells such as proliferation, migration,invasion, angiogenesis and metastasis among others, as well as forstudying effects of anticancer treatments. Such models range from purelyin vitro systems, such as monolayers or anchorage-independent growth insoft agar, to growth in vivo following subcutaneous, intramuscular, orintraperitoneal injection in immunocompromised mice (e.g. Kunz-Schughartet al., Exp Cell Res 2001 266:74-86). However, these experimental modelsof human tumor cell growth do not permit the study of properties oftumor cells related to their growth within the microenvironment ofadjacent normal differentiated human cell tissues and structures and arenot particularly amenable to the investigation of stromal interactions.

It was the emergence of in vivo models using tumor xenografl growth inimmuno-compromised mice, which highlighted the importance of the stromalresponse. However, in the numerous published studies using this model,it has been the murine, rather than the human stromal response, whichhas been the target of investigation or experimental therapeuticintervention. Therefore, the present invention provides multicellularcomposites having a 3-dimensional microarchitecture, the compositescomprising cancer cells of human origin together with a normal humanmicroenvironment derived from human embryonic stem cells. Thus, themulticellular composites of the present invention perfectly simulatetumor tissue within normal tissue in human and may thus be used in atransitional platform between the pre-clinical and the clinicalplatforms for evaluating therapeutic ability of relevant candidates,particularly anticancer drug. In addition, the multicellular compositesof the present invention enable studying the interactions between tumorcells and the surrounding microenvironment of differentiated human celltissues and structures.

Upon successful introduction of cancer tissue or cells into a hostanimal, for example by injection or implantation, neo-vascularization isinduced due to the angiogenic signals generated by the cancer cells. Theresulting new blood vessels are established from cell, such asendothelial cells and smooth muscle cells, which are recruited from thehost animal by the implanted cancer cells. The multicellular compositionof the present invention comprise new blood vessel of human origin whichare formed from human cells recruited from the normal humanmicroenvironment of the multicellular compositions of the invention.

The ability to evaluate arrangement and content of cancer cells in thecontext of the normal tissue surrounding the cancer cells, using thesystem and method of the present invention, has an enormous experimentaland clinical potential. For example, the system and method of thepresent invention may be used for elucidating properties and factorswhich modulate tissue invasion, reactive sclerosis, angiogenesis, andresponses to certain anticancer regimens among others.

It should be recognized that the multicellular composites of the presentinvention, such as teratomas comprising cancer cells and embryoid bodiescomprising cancer cells, may be designed to comprises a specific humantissue, such as a pancreatic tissue, and may also be designed as mixtureof cells lack tissue homogeneity or organization.

The need for a system and method that enable monitoring arrangement andcontent of cancer cells in the context of the normal tissue surroundingthe cancer cells is demonstrated by the following studies. Endostatinwas shown to be a potent anti-angiogenic agent in tumors that were grownin immunocompromised mice (Folkman, Semin Oncol 6, Suppl 16, 15-182002). However, endostatin did not exhibit any inhibitory effect inhuman B-lineage acute lymphoblastic leukemia (B-ALL) that was engraftedwithin the marrow of immunodeficient mice (Eisterer et al, MolecularTherapy 5, 352-9, 2002). The results were non reproducible probablysince in the first case the antiangiogenic agent, endostatin, wasevaluated in a host animal and not in tumors grown in a microenvironmentof human tissue comprising new blood vessels.

The system and method of the present invention are particularlyadvantageous for screening anticancer therapeutic compounds andcompositions comprising thereof. The system and method provided in thepresent invention also allow to select anticancer therapeutic candidatesthat failed to perform anticancer activity when tested in the commonlyused in vitro models or in vivo animal models known in the art.

Another advantage of the system and method is the ability to provide asuitable platform for evaluating the activity of anticancer andimmuno-targeting therapeutic agents, which require for their activity amicroenvironment of normal human tissue.

1. Preferred Modes for Carrying Out the Invention 1.1 Definitions

The term “embryonic stem cells” or “ESC” refers to pluripotent cellsderived from the inner cell mass of blastocysts with the capacity forunlimited proliferation in vitro in the undifferentiated state (Evans etal., Nature, 292:154-6, 1981). Embryonic stem cells can differentiateinto any cell type in vivo (e.g. Nagy, et al., Development, 110:815-821,1990) and into a more limited variety of cells in vitro (e.g. Schmitt,et al., Genes and Development, 5: 728-740, 1991).

The term “adult stem cells” as used herein, refers to cells derived fromdifferentiated human embryonic stem cells, and to multipotential adultprogenitor cells (also known as MAPC; e.g. Nature 418:41-9, 2002) haveextended replicative capacity and a restricted differentiation capacity(partial lineage commitment).

The term “embryoid body” as used herein, describes a population of ESCcells having a 3-dimensional microarchitecture. The population maycomprise undifferentiated ESC and may further comprise differentiatedESC comprising the three major germ cell layers.

The term “teratoma” as used herein refers to a cellular complex having a3-dimensional microarchitecture which develops from undifferentiatedhuman embryonic stem cells implanted into a suitable animal host such asgenetically immunocompromised mice. The teratoma comprisesdifferentiated cell types which represent the major germline derivedlineages. The teratoma comprises of derivatives of all three major germcell layers (ectoderm, mesoderm, endoderm)

The term “multicellular system” as used herein refers to a cellularcomposition comprising human embryonic stem cells and cancer cellswherein the human embryonic stem cells are cultured in conditionssuitable for differentiation and formation of embryoid bodies, in vitro,or teratomas, in vivo, thus generating a microenvironment of normalhuman tissue for the cancer cells injected therein. The terms “mixedculture”, “coculture” and “multicellular system” may be usedinterchangeably.

The term “anticancer effect” as used herein, refers to a biologicaleffect which can be manifested by a decrease in tumor size, a decreasein the number of metastases, an increase in life expectancy, oramelioration of various physiological symptoms associated with thecancerous condition. An “anticancer effect” can be manifested in thetreatment of acute cancer as well as in cancer prophylaxis. Atherapeutic agent that is capable of exerting an anticancer effect istermed herein an “an anticancer agent” or a “therapeutic agent”.

1.2 Embryonic Stem Cells Culture

According to one embodiment, the present invention providesmulticellular composition implanted within an immunocompromised animal,comprising cancer cells within a normal human tissue derived fromdifferentiated human embryonic stem cells, wherein the cancer cellsmaintain their abnormal phenotype including the ability to induceangiogenic activity in the normal human tissue. Multicellularcomposition comprising cancer cells within a normal human tissue derivedfrom differentiated human embryonic stem cells is described by thepresent inventors and coworkers and published after the priority date ofthe present application (Tzukerman et al., Proc. Natl. Acad. Sci. USA2003 Nov. 11; 100(23):13507-12, e-pub. 2003 Oct. 22).

The method of the present invention comprises utilization of embryonicstem cells capable of producing progenitors which can proliferate anddifferentiate into a desired population of committed precursors or intofully differentiated cells.

Preferably, the method of the present invention utilizes human embryonicstem cells which develop into teratomas when grown withinimmunocompromised mice.

Embryonic stem cells display the following characteristics:

1. Normal diploid karyotype.

2. Capacity for indefinite propagation in the undifferentiated statewhen grown on a feeder layer.

3. Telomerase enzyme activity in the undifferentiated state.

4. Formation of multicellular aggregates, yielding outgrowths containingmultiple identifiable differentiated cell types, including derivativesof the three major germ cell layers (ectoderm, mesoderm, endoderm) uponrelease from the feeder layer.

Detailed procedures for culturing pluripotent human embryonic stem cellsare known in the art, e.g. U.S. Pat. No. 6,280,718.

Methods for separating stem cells from dedicated cells are known in theart (e.g. U.S. Pat. No. 5,914,108).

Embryonic stem cells display the innate property to differentiatespontaneously. In order to enrich the population of the undifferentiatedESC of the invention and to maintain its homogeneity, the innatespontaneous differentiation of these cells has to be suppressed. Methodsfor suppressing differentiation of embryonic cells, particularly ofhuman embryonic stem cells, may include culturing the undifferentiatedembryonic cells on a feeder layer, such as of murine fibroblasts, alsotermed hereinafter “mouse embryonic fibroblasts” feeder layer or “MEFs”,or in media conditioned by certain cells (e.g. U.S. Pat. No. 4,016,036).

MEF cells are commonly derived from day 12-13 mouse embryos in a mediumconsisting of DMEM supplemented with about 10% fetal bovine serum, about2 mM 1-glutamine, and antibiotics, for example, 100 units/ml penicillinand 100 mg/ml streptomycin. MEF cells may be cultured on dishes, whichare first coated with about 0.1% gelatin solution for one or more daysin a 37° C./5% CO₂ incubator. The gelatin solution is then removed andthe dishes are coated with irradiated MEF cells. The MEF cells may beirradiated with 5500 cGy from a cesium source prior to plating in thedish. The MEFs are added at a density of about 5·10⁴ cells/ml, 2.5ml/well. The plates coated with MEFs are then placed in an incubator forone or more days until addition of human ES cells.

Human ES cells may be passed onto new MEFs, preferably at 3-8 dayintervals, when cell density and morphologic appearance ofdifferentiation is appropriate. The time of passage to a new MEF dependson cell density and morphologic appearance of differentiation. Forpassage, the medium in a well of hES cells is removed and mediumcontaining about 1 mg/ml collagenase IV in DMEM is added.

Any cell culture media that can support the growth and differentiationof human embryonic stem cells, can be used with the present invention.Such cell culture media include, but are not limited to Basal MediaEagle, Dulbecco's Modified Eagle Medium, Iscove's Modified Dulbecco'sMedium, McCoy's Medium, Minimum Essential Medium, F-10 NutrientMixtures, OPTI-MEM® Reduced-Serum Medium, RPMI Medium, andMacrophage-SFM Medium or combinations thereof. The culture medium can besupplied in either a concentrated (e.g.: 10×) or non-concentrated form,and may be supplied as a liquid, a powder, or a lyophilizate. Culturemedia is commercially available from many sources, such as GIBCO BRL(MD, USA) and Sigma (MO, USA)

According to a certain embodiment, the medium for culturingnondifferentiated human embryonic stem cells may consist of 80% knockoutDulbecco's modified Eagle's medium supplemented with 20% serumreplacement, 0.1 mM (3-mercaptoethanol, 1% non-essential amino acidstock. Preferably, human recombinant basic fibroblast growth factor(bFGF) is added to the culture medium.

At the time of passaging the hESC to the MEF coated plates, if there arecolonies of hES cells showing morphologic appearance of differentiationprior to cell passage, these colonies may be removed by gentle scrapingwith a pulled glass pipette. This is done with observation through adissecting microscope. After removal of the differentiated cells, theremaining colonies may be passaged.

Alternatively, maintaining undifferentiated ESC in the laboratory,particularly mouse ESC, may be achieved by the addition of adifferentiation inhibitory factor (commonly referred to as leukemiainhibitory factor or LIF) in the culture medium to prevent spontaneousdifferentiation (e.g. Pease, et al., Dev. Biol., 141: 344-352, 1990).LIF is a secreted protein and can be provided by maintaining embryonicstem cells on a feeder layer of cells that produce LIF (Robertson,Teratocarcinomas and Embryonic Stem Cells: A Practical Approach,Washington, D.C.: IRL Press, 1987) or by the addition of purified LIF(e.g. Pease, et al., Exp. Cell Res., 190: 209-211, 1990) to the mediumin the absence of feeder layers.

International Patent Application WO 99/20741 describes methods andmaterials for growing pluripotent stem cells, including human embryonicstem cells, in the absence of feeder cells, on an extracellular matrixwith a nutrient medium. Suitable are fibroblast matrices prepared fromlysed fibroblasts or isolated matrix component from a number of sources.The nutrient medium may contain sodium pyruvate, nucleosides, and one ormore endogenously added growth factors, such as bFGF, and may beconditioned by culturing with fibroblasts.

Differentiation of embryonic stem cells into a heterogeneous mixture ofcells occurs spontaneously by removing the conditions which suppressdifferentiation, for example by removing MEFs or LIF, by generating ateratoma, or by other manipulations of the culture conditions(Outierrez-Ramos, et al., Proc. Nat. Acad. Sci., 89: 9111-9175, 1992).

Differentiation pattern of embryonic stem cell may depend on theembryonic stem cell line and may even vary, in the same embryonic stemcell line, between different laboratories.

A method for selective ex-vivo expansion of stem cells is disclosed inU.S. Pat. No. 6,479,261. The method comprises the steps of separatingstem cells from other cells and culturing the separated stem cells in agrowth media comprising a modified human interleukin-3 polypeptidehaving at least three times greater cell proliferative activity thannative human interleukin-3, in at least one assay selected from thegroup consisting of: AML cell proliferation, TF-1 cell proliferation andMethylcellulose assay. Methods for the treatment of a patient having ahemapoetic disorder are also disclosed in U.S. Pat. No. 6,479,261. Thesemethods comprise removal of stem cells from a patient following ex-vivoselection of stem cells and expansion of the selected cells.

A method for obtaining Human hematopoietic stem cells by separatingthese cells from dedicated cells is disclosed in U.S. Pat. No.5,914,108. The separated stem cells may than be maintained byregeneration in an appropriate growth medium.

A method to produce an immortalized mammalian ESC population isdisclosed in U.S. Pat. No. 6,110,739. The method comprising: (a)transforming an embryonic stem cell population with an immortalizinggene to create a transformed stem cell population; (b) culturing saidtransformed stem cell population under effective conditions to produce atransformed embryoid body cell population; and (c) incubating saidtransformed embryoid body cell population under conditions suitable toobtain an immortalized cell population that differentiates into cellularlineages comprising primitive erythroid cells and definitive erythroidcells.

Methods for in vitro culturing of embryonic cell populations,particularly pluripotent human embryonic stem cells, utilizingcombinations of growth factors for propagation and immortalization ofthese cells, are known in the art as for example disclosed in U.S. Pat.Nos. 5,690,926 and 6,110,739 and European Patent No. 380646, among manyothers.

An example for a purified preparation of pluripotent human embryonicstem cells is disclosed in U.S. Pat. No. 6,200,806. This preparation (i)will proliferate in an in vitro culture for over one year, (ii)maintains a karyotype in which the chromosomes are euploid and notaltered through prolonged culture, (iii) maintains the potential todifferentiate to derivatives of endoderm, mesoderm, and ectoderm tissuesthroughout the culture, and (iv) is inhibited from differentiation whencultured on a fibroblast feeder layer. The following cell surfacemarkers characterize the purified preparation: SSEA-1 (−), SSEA-4 (+),TRA-1-60 (+), TRA-1-81 (−) and alkaline phosphatase (+).

Induction of differentiation in ES cells, preferably a controlledinduction towards a specific cell lineage, is achieved for example byremoving the differentiation-suppressing element, e.g. the feeder layer,from the culture. The embryonic stem cells may be placed in a culturevessel to which the cells do not adhere.

To effectively control the consequent differentiation, the cells must bein a homogeneous state. U.S. Pat. No. 6,432,711 provides a method forobtaining embryonic stem cells which are capable of differentiatinguniformly into a specific and homogeneous cell line. The methodcomprises culturing embryonic stem cells under conditions which promotegrowth of the cells at an optimal growth rate. The embryonic stem cellsthen are cultured under conditions which promote the growth of the cellsat a rate which is less than that of the optimal growth rate, and in thepresence of an agent which promotes differentiation of the embryonicstem cells into the desired cell line. According to this method, agrowth rate which is less than the optimal growth rate, is a growth ratefrom about 10% to about 80%, preferably from about 20% to about 50%, ofthe maximum growth rate for embryonic stem cells.

The desired cell types may be further enriched and/or purified usingselection markers and gene trapping based on the methods disclosed inU.S. Pat. No. 5,602,301.

For example, the embryonic stem cells may be placed in a culture vesselto which the cells do not adhere. Examples of non-adherent substratesinclude, but are not limited to, polystyrene and glass. The substratemay be untreated, or may be treated such that a negative charge isimparted to the cell culture surface. In addition, the cells may beplated in methylcellulose in culture media, or in normal culture mediain hanging drops. Media which contains methylcellulose is viscous, andthe embryonic stem cells cannot adhere to the dish. Instead, the cellsremain isolated, and proliferate, and form aggregates.

In a certain embodiment, the methods of the present invention utilizeteratomas derived from differentiated human embryonic stem cells. Humanembryonic stem cells when implanted into immunocompromised mice developcharacteristic teratomas which contain numerous complex andmulti-layered tissue structures, comprising differentiated cell typesarising out of all the major germ line derived lineages.

Embryonic stem cell lines derived from human blastocysts have thedevelopmental potential to form derivatives of all three embryonic germlayers even after prolonged culture.

In a certain alternative embodiment the multicellular composition of thepresent invention comprises the H-9.1 clone of undifferentiated humanembryonic stems cells (Amit et al., Dev. Biol. 227, 271-8, 2000). Aftera prolonged culture this clone was shown to maintain the followingcharacteristics: (1) active proliferation, (2) expression of high levelsof telomerase, and (3) maintenance of normal karyotypes. High-passage ofthe H9.1 cells form teratomas in SCID-beige mice that includedifferentiated derivatives of all three embryonic germ layers. Othertypes of human embryonic stem cells may also be utilized to generate themulticellular systems of the present invention, for example, H1, H9,H9.2 and the like.

1.3 Multicellular Compositions and Formation Thereof

According to one embodiment the present invention provides amulticellular composition comprising at least one embryoid bodycomprising human embryonic stem cells together with human cancer cells.According to another embodiment the present invention provides amulticellular composition comprising normal human tissue derived fromdifferentiated human embryonic stem cells and cancer cells.

The multicellular compositions of the present invention comprise cancercells. The cancer cells may be established cell lines or primary cells.Preferably, the cancer cells are of a human origin. The cancer cells maybe derived from solid malignant tumors, non-solid malignant tumors, andhematologic cancers. Particular embodiments of the invention includecancer cells selected from the group consisting of: prostate cancer,breast cancer, ovarian cancer, lung cancer, melanoma, renal cancer,bladder cancer, fibrosarcoma, hepatocellular carcinoma, osteocarcinoma,primary ductal carcinoma, giant cell sarcoma, ductal carcinoma,Hodgkin's disease, colorectal carcinoma, lymphoma, transitional cellcarcinoma, uterine sarcoma, adenocarcinoma, plasmacytoma, epidermoidcarcinoma, Burkitt's lymphoma, Ewing's sarcoma, gastric carcinoma,squamous cell carcinoma, neuroblastoma, rhabdomyosarcoma.

According to yet another embodiment the cancer cells of themulticellular composition of the present invention maintain the abilityto at least one of the following: invade the normal humanmicroenvironment, induce angiogenic activity in the normal humanmicroenvironment, elicit formation of new human blood vessels within thenormal human microenvironment

The human origin of the newly formed blood vessels may be verified usingcell surface markers as are well known in the art. For example, vonWillebrand factor and smooth muscle cells-actin.

The multicellular compositions of the present invention may be generatedin vitro or in vivo. According to one embodiment the multicellularcompositions are maintained in culture. According to another embodiment,the multicellular compositions are implanted within a host animal.According to some embodiments the multicellular compositions areimplanted intraperitoneally and maintained in ascites form. According tosome embodiments the embryoid bodies are implanted into a predeterminedsite within the host animal and develop into teratomas. According tosome embodiments the embryoid bodies are occluded within barriermembranes prior to implantation.

According to one embodiment the present invention provides a method forthe formation of multicellular compositions comprising cancer cells ofhuman origin within a normal human tissue derived from human embryonicstem cells, comprising:

-   -   (a) culturing hESC in conditions which promote formation of        embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body;        and    -   (d) determining the presence of cancer cells within said at        least one embryoid body.

According to another embodiment, the method further comprises:

-   -   (e) injecting said at least one embryoid body into a defined        locus in a host animal.

According to another embodiment, the method further comprises:

-   -   (f) determining the formation of at least one teratoma in the        locus of injection.

According to an alternative embodiment, step (e) is replaced with:

-   -   (g) injecting said at least one embryoid body into the        peritoneal cavity of a host animal.

According to an alternative embodiment, step (e) is replaced with:

-   -   (h) injecting said at least one embryoid body into the host        animal, wherein said at least one embryoid body is occluded        within a barrier membrane prior to implantation.

According to some embodiment, human embryonic stem cells when implantedinto immunocompromised mice develop characteristic teratomas whichcontain numerous complex and multi-layered tissue structures, comprisingdifferentiated cell types arising out of all the major germ line derivedlineages as described hereinabove.

According to some embodiments, cancer cells are injected into teratomas,in vivo, about 2 months after injection of the hESC into theimmunodeficient mice.

According to yet another embodiment, the present invention provides amethod for the formation of multicellular compositions comprising cancercells of human origin within a normal human tissue derived from humanembryonic stem cells, in vivo, comprising:

-   -   (a) injecting undifferentiated human embryonic stem cells into a        host animal;    -   (b) determining the formation of at least one teratoma in the        locus of injection;    -   (c) injecting cancer cells into the at least one teratoma of        (b); and    -   (d) determining the presence of cancer cells within the at least        one teratoma.

The presence of cancer cells within teratomas and within embryoid bodiesis determined can take place a few days after injection of the cancercells into the teratomas or the embryoid bodies. Preferably, thepresence of cancer cells within a teratoma is determined a few weeks, 1to 4 weeks, after injection of the cancer cells into the teratoma.According to some embodiments, for the purpose of detection teratomas orembryonic bodies are harvested and prepared for histologic analysis.According to alternative embodiments, teratomas may be detected by anact of palpation or by imaging methods, preferably 2 to 7 weeks afterinjection.

According to alternative embodiments, the cancer cells are transfectedwith a green fluorescent reporter fusion protein (GFP), which enables totrack them within the surrounding microenvironment of normaldifferentiated human cells and tissue. Thus, the presence of the cancercells in a teratoma or in embryoid bodies is preferably achieved byexposing microsections of the teratoma or the embryoid bodies to antiGFP antibodies, and a suitable detection system.

The presence of cancer cells is typically monitored in a population ofrepresentative teratomas or embryoid bodies and is compared to thepresence of cancer cells in control teratomas or embryoid bodies whichdid not receive an injection of cancer cells.

According to yet another embodiment, the undifferentiated humanembryonic stem cells are injected into a defined locus in the hostanimal. According to yet another embodiment, the undifferentiated humanembryonic stem cells are injected into the peritoneal cavity of a hostanimal. According to yet another embodiment, the undifferentiated humanembryonic stem cells are occluded within a barrier membrane prior toimplantation in a host animal.

According to certain embodiments, the hESC are initially cultured on3-dimension polymer-based in vitro models (Levenberg et al., Proc. Natl.Acad. Sci. USA, 100:12741-12746, 2003) and the cancer cells aremicroinjected in the 3D structures formed within the 3-dimensionpolymer-based models.

Various means for injections of cells for the purpose of implantationwithin a suitable host animal are known in the art. Cells may beinoculated subcutaneously, intravenously, intramuscularly,intraperitoneally or inserted via other means of injection into thedesired site of cells implantation. A preferred site for cellinoculation in immunocompromised mice is the hindlimb's muscle. Analternative method of implantation include use of barrier membraneswhich occlude the multicellular compositions and are then implanted inthe host animal.

For the purpose of implantation using barrier membranes, hESC and thecancer cells are initially cultured in the presence of a barriermembrane. The barrier membrane may be commercial membranes andbiocompatible membranes as known in the art (e.g. Teflon membranes,Resolut® LT and Biofix®). Preferably, the membrane are impermeable tocertain cells, such as cells of the immune system and bacteria, and maybe further impermeable to antibodies and other factors that can causeimplant rejection. The membranes may be composed of a dense polymericlayer coupled with nonwoven (e.g. Resolut® LT) or woven (e.g. Biofix®)fibers.

Several types of immunocompromised mice that are suitable for theteaching of the present invention are known in the art includingdifferent kinds of athymic nude mice and Severe Combined ImmunoDeficient (SCID) mice. The multicellular composition of the presentinvention exemplified hereinbelow is implanted, by a way of non-limitingexample, in SCID/beige mice.

1.4 Genetic Modifications

According to some embodiments, at least some of the cells of themulticellular compositions of the invention are genetically modified.According to some embodiments, the cancer cells, or at least some of thecancer cells, are genetically modified. According to other embodiments,the hESC, or at least some of the hESC, are genetically modified.

The genetically modified cells comprise a construct or a vectorcomprising at least one exogenous polynucleotide. The construct or thevector may further comprise at least one regulatory element. The atleast one regulatory element may be selected from the group consistingof: promoter, enhancer, post transcriptional element, initiation codon,stop codon, polyadenylation signal and selection marker. The exogenouspolynucleotide sequence may be operably linked to expression controlsequences.

According to one embodiment, the exogenous polynucleotide is stablyintegrated into the genome of said at least some cells. Thus, the atleast some transformed cells may constitutively express the exogenouspolynucleotide. According to yet another embodiment, the exogenouspolynucleotide is transiently expressed by the at least some cells.

The regulatory element may serve to confer functional expression of theexogenous polynucleotide. For example, expression of the exogenouspolynucleotide may be produced by activating the regulatory nucleotidesequence.

According to some embodiments, the exogenous polynucleotide comprises apromoter sequence that controls the expression thereof. The promoter maybe any array of DNA sequences that interact specifically with cellulartranscription factors to regulate transcription of the downstream gene.The promoter may be derived from any organism, such as bacteria, yeast,insect and mammalian cells and viruses. The selection of a particularpromoter depends on what cell type is to be used to express the proteinof interest. Examples of the promoter include, but are not limited to,E. coli lac and trp operons, the tac promoter, the bacteriophage λβ^(p)Lpromoter, bacteriophage T7 and SP6 promoters, β-actin promoter, insulinpromoter, human cytomegalovirus (CMV) promoter, HIV-LTR (HIV-longterminal repeat), Rous sarcoma virus RSV-LTR, simian virus SV40promoter, baculoviral polyhedrin and p10 promoter. The promoter may alsobe an inducible promoter that regulates the expression of downstreamgene in a controlled manner, such as under a specific condition of thecell culture. Examples of inducible promoters include, but are notlimited to, the bacterial dual promoter (activator/repressor expressionsystem) which regulates gene expression in mammalian cells under thecontrol of tetracyclines (Gossen et al., Proc. Natl. Acad. Sci. USA, 89,5547-5551, 1992) and promoters that regulate gene expression under thecontrol of factors such as heat shocks, steroid hormones, heavy metals,phorbol ester, the adenovirus E1A element, interferon, or serum.

According to another embodiment, the construct or vector comprise aselection marker. Selection markers are well known in the art, and theselection technique may vary depending upon the selection marker used.According to one embodiment, the selection marker is a gene inducingantibiotic resistance, enabling the survival of the transgenic cells ina medium containing the antibiotic as a selection agent. According toanother embodiment, the selection marker is a reporter gene. Thereporter gene can encode for a fluorescent protein, a chemiluminescentprotein, a protein having a detectable enzymatic activity and the like,as is known to a person skilled in the art.

Genes that encode easily assayable marker polypeptides are well known inthe art. In general, such gene are not present or expressed by therecipient organism or tissue and may encode a polypeptide whoseexpression is manifested by some easily detectable property, e.g.phenotypic change or enzymatic activity and thus when co-transfectedinto recipient cells with a gene of interest, provide a means to detecttransfection and other events.

Among genes appropriate to use according to the present invention, arethose that encode fluorescent proteins. Of interest are fluorescentcompounds and proteins, such as naturally fluorescent phycobiliproteins.Also are the fluorescent proteins that are present in a variety ofmarine invertebrates, such as the green and blue fluorescent proteins,particularly the green fluorescent protein (GFP) of Aequorea Victoriaand the red fluorescence protein (RFP) of Discosoma sp. The greenfluorescent proteins constitute a class of chromoproteins found onlyamong certain bioluminescent coelenterates. These accessory proteins arefluorescent and function as the ultimate bioluminescence emitter inthese organisms by accepting energy from enzyme-bound, excited-stateoxyluciferin (e.g., see Ward et al. Biochemistry 21:4535-40, 1982).Transfection of the cells may be transient or stable and may be appliedwith a vector that expresses the desired gene under the control of apromoter. The transient transfectants may also constitute the basis forselection of stable transfectants as exemplified herein below.

By way of a non-limiting example, the multicellular compositions maycomprise HEY-ovarian cancer cells stably transfected so as toconstitutively express a nuclear histone H2A-green fluorescent reporterfusion protein (HEY-GFP).

By way of another non-limiting example, the multicellular compositionsmay comprise HEY-ovarian cancer cells stably transfected so as toconstitutively express red fluorescence protein (RFP) fused with threecopies of the nuclear localization signal (NLS) of the simian virus 40large T-antigen.

According to yet another embodiment, the multicellular compositions ofthe present invention comprise cancer cells that are transfected with amarker gene in order to enable detection of these cells within themulticellular compositions, particularly, to distinguish theses cancercells from the normal environment using straight forward detectionmeans. Marking the cancer cells of the compositions of the presentinvention, for example, with a fluorescent protein, is especially usefulfor determining the invasiveness of these cells within the normal humanmicroenvironment.

Other methods may be applied to determine the presence of cancer cellsin the systems of the present invention and to determine theinvasiveness of these cells to the surrounding environment. For example,immunohistochemistry may be utilized with antibodies which bind epitopesspecific to the cancer cells. Alternatively, in-situ hybridization withprobes that bind mRNAs characteristic of the cancer cells may be used.

Introduction of synthetic polynucleotide into a target cell can involveone or more of non-viral and viral vectors, cationic liposomes,retroviruses, and adenoviruses such as, for example, described inMulligan, R. C., (1993 Science 260:926). Vectors are employed withtranscription, translation and/or post-translational signals, such astargeting signals, necessary for efficient expression of the genes invarious host cells into which the vectors are introduced. Such vectorsare constructed and transformed into host cells by methods well known inthe art. See Sambrook et al., Molecular Cloning: A Laboratory Manual,Cold Spring Harbor (1989).

Numerous methods for evaluating the effectiveness of transfection areknown in the art. The effectiveness of transfection with a vectorcomprising an EGFP reporter gene may be monitored by straightforwardfluorescence measurements as exemplified hereinbelow.

1.5 Methods for Screening Therapeutic Agents and Evaluating EfficacyThereof

The experimental platforms known in the art for screening of anticancertherapeutic agents circumvents two major limitations, as follows:

(a) Loss of anticancer therapies at the phase I stage: A number oftherapies, which have been tested in models based on experimentalanimals, have gone on for testing in phase I clinical trials.Unanticipated human cytotoxicity side effects in phase I clinicaltrials, have resulted in a high dropout percentage. In many cases, thisdropout is a result of unanticipated cyto-toxicity to normal humantissues. Thus, use of the multicellular composition of the presentinvention for testing the efficacy of anticancer therapeutic agents maypreempt the risk and expenditure related a phase I clinical trial, byrevealing unanticipated untoward effects which may be only observed inwhen cancer cells are present in a normal human environment; and

(b) Unwanted exclusion of anticancer therapies from proceeding to phaseI trials: Currently, studies in experimental animals sometimesmisleadingly yield results which preclude progression to human trials(such as the development of antiangiogenic agents). However, it is knownthat untoward effects or toxicities in animal model systems may not beapplicable to a human system. Nevertheless, untoward effects in ananimal system are often the basis for precluding progression to apotentially informative set of clinical trials beginning with a phase Itrial. Use of the multicellular composition of the present invention fortesting therapeutic agents may offer and advantageous platform byshowing that untoward effects or cytotoxic effects in experimentalanimals are not necessarily applicable in a human co-culture system.

Thus, the present invention provides multicellular systems of embryoidbodies or teratomas, which contain cancer cells therein. In effect, thisgenerates a system in which a human cancer cell type of interest isgrowing in the context of mixed culture of differentiating anddifferentiated normal human cell types. This normal humanmicroenvironment contains elements representing all of the differentgermline derivatives, including mature and immature fully differentiatedstructures. Thus, the interaction of the co-cultured cancer cells, whichhave been incorporated within the normal human microenvironment, can besubjected to experimental scrutiny, including for example, screening anddetermining the efficacy of chemotherapeutic agents, pro-apoptoticagents, anti-angiogenic agents, and a variety of established and novelanticancer therapies.

Use of multipotent neural stem cells and their progeny for the screeningof drugs and other therapeutic agents is disclosed in U.S. Pat. No.6,294,346. This patent disclosed a culture method for determining theeffect of a therapeutic agent on multipotent neural stem cell progeny,wherein the multipotent neural stem cells are obtained from normalneural tissue or from a donor afflicted with a disease such asAlzheimer's Disease, Parkinson's Disease or Down's Syndrome.Additionally, a method of screening the effects of therapeutic agents ona clonal population of neural cells is provided. The technology providesan efficient method for the generation of large numbers of pre- andpost-natal neural cells under controlled, defined conditions.

According to one embodiment, the present invention provides a method ofscreening therapeutic agents, in vivo, comprising:

-   -   (a) injecting undifferentiated human embryonic stem cells into a        host animal;    -   (b) determining the formation of at least one teratoma in the        host animal;    -   (c) injecting cancer cells into the at least one teratoma;    -   (d) determining the presence of cancer cells within said at        least one teratoma;    -   (e) treating the host animal having said at least one teratoma        with a composition comprising a candidate therapeutic agent; and    -   (f) determining whether the therapeutic agent has an effect on        said at least one teratoma.

According to an alternative embodiment, the at least one embryoid bodyis injected into a site selected from a defined locus in said hostanimal and the peritoneal cavity of a host animal.

According to another alternative embodiment, step (a) is replaced with:

-   -   (g) injecting into a host animal undifferentiated human        embryonic stem cells occluded within a barrier membrane.

According to yet another embodiment, treating the host animal isperformed by topical administration of said therapeutic agent to said atleast one teratoma.

According to certain alternative embodiment, the method comprises:

-   -   (a) culturing hESC in conditions which promote generation of        embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body;    -   (d) determining the presence of cancer cells within said at        least one embryoid body;    -   (e) injecting said at least one embryoid body into a host        animal;    -   (f) treating the host animal with a composition comprising a        candidate therapeutic agent; and    -   (g) determining whether the candidate therapeutic agent has an        effect on said at least one embryoid body.

According to an alternative embodiment, the at least one embryoid bodyis injected into a site selected from a defined locus in said hostanimal and the peritoneal cavity of a host animal.

According to an alternative embodiment, step (e) is replaced with:

-   -   (h) injecting into the host animal said at least one embryoid        body, wherein said at least one embryoid body is occluded within        a barrier membrane.

According to another embodiment, the after step (e) and before step (f)the method further comprises determining the formation of a teratomafrom the at least one embryoid body.

According to an alternative embodiment, step (g) comprises determiningwhether said at least one therapeutic agent has an effect on theteratoma.

According to yet another embodiment, treating the host animal isperformed by topical administration of said therapeutic agent to said atleast one teratoma.

According to yet another embodiment, the present invention provides amethod for screening, in vitro, the effect of a therapeutic agent oncancer cells comprising:

-   -   (a) culturing human embryonic stem cells in conditions which        promote generation of embryoid bodies;    -   (b) determining the formation of at least one embryoid body in        the culture of (a);    -   (c) injecting cancer cells into the at least one embryoid body;    -   (d) determining the presence of cancer cells within said at        least one embryoid body;    -   (e) contacting said at least one embryoid body to a composition        comprising a therapeutic agent; and    -   (f) determining whether the therapeutic agent has an effect on        the at least one embryoid body.

According to yet another embodiment, determining the effect of thetherapeutic agent on the multicellular composition comprises evaluatingat least one of the following parameters: cell proliferation, celldifferentiation, invasiveness of the cancer cells, angiogenesis andapoptosis.

According to another embodiment, the therapeutic agent is selected fromthe group consisting of: a cytotoxic compound, a cytostatic compound,anticancer drug, an antisense compound, an anti-viral agent, an agentinhibitory of DNA synthesis and function and an antibody.

According to yet another embodiment, the therapeutic agent is conjugatedto an agent selected from the group consisting of: imaging agent and acarrier.

According to yet another embodiment, the imaging agent is selected from,but not restricted to, paramagnetic particles: gadolinium, yttrium,lutetium and gallinum; radioactive moieties: radioactive indium, rheniumand technetium; and dyes: fluorescin isothiocyanate (FITC), greenfluorescent protein (GFP), cyan fluorescent protein (CFP), rhodamine I,II, III and IV, rhodamine B, and rosamine.

According to yet another embodiment, the therapeutic agent is animmunotherapeutic agent of human origin, selected from the groupconsisting of: an antibody, a cell of the immune system, such as anatural killer cell or a T-helper cell, a cytokine, a chemokine.

According to yet another embodiment, the therapeutic agent comprises atleast one oligonucleotide, selected from antisense, sense nucleotidesequence, short interfering RNA, ribozyme and aptomer.

In recent years, advances in nucleic acid chemistry and gene transferhave inspired new approaches to engineer specific interference with geneexpression.

Antisense technology has been one of the most commonly describedapproaches in protocols to achieve gene-specific interference. Forantisense strategies, stoichiometric amounts of single-stranded nucleicacid complementary to the messenger RNA for the gene of interest areintroduced into the cell.

International Publication No. WO 02/10365 provides a method for genesuppression in eukaryotes by transformation with a recombinant constructcontaining a promoter, at least one antisense and/or sense nucleotidesequence for the gene(s) to be suppressed, wherein thenucleus-to-cytoplasm transport of the transcription products of theconstruct is inhibited. In one embodiment, nucleus-to-cytoplasmtransport is inhibited by the absence of a normal 3′ UTR. The constructcan optionally include at least one self-cleaving ribozyme. Theconstruct can also optionally include sense and/or antisense sequencesto multiple genes that are to be simultaneously downregulated using asingle promoter. Also disclosed are vectors, plants, animals, seeds,gametes, and embryos containing the recombinant constructs.

European Patent Application No. 0223399 A1 describes methods for the useof genetic engineering technology in plants to achieve useful somaticchanges to plants, not involving the expression of any exogenousproteins, but instead controlling the expression of an endogenousprotein or other DNA or RNA factor naturally introduced into the plantcells through outside agents, such as agents of disease or infection.

Antisense has recently become accepted as therapeutic moieties in thetreatment of disease states. For example, U.S. Pat. No. 5,098,890 isdirected to antisense oligonucleotide therapies for certain cancerousconditions. U.S. Pat. No. 5,135,917 provides antisense oligonucleotidesthat inhibit human interleukin-1 receptor expression. U.S. Pat. No.5,087,617 provides methods for treating cancer patients with antisenseoligonucleotides. U.S. Pat. No. 5,166,195 provides oligonucleotideinhibitors of HIV. U.S. Pat. No. 5,004,810 provides oligomers capable ofhybridizing to herpes simplex virus Vmw65 mRNA and inhibitingreplication. U.S. Pat. No. 5,194,428 provides antisense oligonucleotideshaving antiviral activity against influenza virus. U.S. Pat. No.4,806,463 provides antisense oligonucleotides and methods using them toinhibit HTLV-III (human T-cell lymphotropic virus type III, known alsoas HIV) replication. Antisense oligonucleotides have been safelyadministered to humans and several clinical trials of antisenseoligonucleotides are presently underway. It is, thus, established thatoligonucleotides can be useful therapeutic instrumentalities and thatthe same can be configured to be useful in treatment regimes fortreatment of cells and animals, especially humans.

Aptamers are specifically binding oligonucleotides fornon-oligonucleotide targets that generally bind nucleic acids. The useof single-stranded DNA as an appropriate material for generatingaptamers is disclosed in U.S. Pat. No. 5,840,567. Use of DNA aptamershas several advantages over RNA including increased nuclease stability,in particular plasma nuclease stability, and ease of amplification byPCR or other methods. RNA generally is converted to DNA prior toamplification using reverse transcriptase, a process that is not equallyefficient with all sequences, resulting in loss of some aptamers from aselected pool.

The methods of the invention may be further utilized for screening shortinterfering RNAs (siRNAs; Fire et al., Nature 391:806-811, 1998). RNAinterference refers to the process of sequence-specificpost-transcriptional gene silencing in animals mediated by siRNAs. Thecorresponding process in plants is commonly referred to aspost-transcriptional gene silencing or RNA silencing. The process ofpost-transcriptional gene silencing is thought to be an evolutionarilyconserved cellular defense mechanism used to prevent the expression offoreign genes and is commonly shared by diverse flora and phyla.

RNA interference is a phenomenon in which double stranded RNA (dsRNA)reduces the expression of the gene to which the dsRNA corresponds. Thephenomenon of RNAi was subsequently proven to exist in many organismsand to be a naturally occurring cellular process. The RNAi pathway canbe used by the organism to inhibit viral infections, transposon jumpingand to regulate the expression of endogenous genes (e.g. Zamore PD., NatStruct Biol. 8(9):746-750, 2001).

International Publication No. WO 00/01846 discloses methods foridentifying specific genes responsible for conferring a particularphenotype in a cell using specific dsRNA molecules. InternationalPublication No. WO 01/29058 discloses specific genes involved indsRNA-mediated RNAi. International Publication No. WO 99/07409 disclosesspecific compositions consisting of particular dsRNA molecules combinedwith certain anti-viral agents. International Publication No. WO99/53050 discloses certain methods for decreasing the phenotypicexpression of a nucleic acid in plant cells using certain dsRNAs.

International Publication No. WO 01/49844 discloses specific DNAconstructs for use in facilitating gene silencing in targeted organisms.

International Publications Nos. WO 02/055692, WO02/055693, and EP1144623 B1 disclose methods for inhibiting gene expression using RNAi.International Publications Nos. WO 99/49029 and WO01/70949, and AU4037501 describe certain vector expressed siRNA molecules. U.S. Pat. No.6,506,559, discloses methods for inhibiting gene expression in vitrousing certain siRNA constructs that mediate RNAi. U.S. Pat. No.5,681,747 discloses methods for inhibiting human-PKCα expression with anoligonucleotide specifically hybridizable to a portion of the3′-untranslated region of PKCα.

According to yet another embodiment, the effect of said therapeuticagent on the at least one teratoma is evaluated by way of comparison tothe effect exerted by said therapeutic agent on at least one otherteratoma generated by the teaching of the present invention and which isessentially similar to the at least one teratoma, wherein the at leastone other teratoma is implanted in a non-treated suitable host animal.According to yet another embodiment, the effect of said therapeuticagent on the at least one teratoma is evaluated by way of comparison tothe effect exerted by said therapeutic agent on cancer cells that areimplanted in the same or different host animal directly and not withinteratomas.

According to yet another embodiment, determining the effect of thetherapeutic agent on the multicellular composition comprises evaluatingat least one of the following parameters: cell proliferation, celldifferentiation, invasiveness of the cancer cells, angiogenesis andapoptosis on the arrangement and content of cancer cells.

According to yet another aspect, the present invention provides a methodfor evaluating treatment efficacy of therapeutic agents, including butnot limited to anticancer drugs, immunotherapeutic drugs and agents forgene therapy, utilizing multicellular compositions comprising normalhuman tissue together with cancer cells.

According to one embodiment, the present invention provides a method forevaluating treatment efficacy of therapeutic agents, comprisingcontacting a plurality of multicellular compositions with a therapeuticagent and assessing the damage caused by the therapeutic agent to thenormal human tissue.

According to another embodiment, the present invention provides a methodfor evaluating treatment efficacy of therapeutic agents, comprisingcontacting a plurality of multicellular compositions with a therapeuticagent and assessing the damage caused by the therapeutic agent to thecancer cells.

According to yet another embodiment, the damage caused by thetherapeutic agent is assessed by evaluating at least one of theparameters selected from the group consisting of: cell proliferation,cell differentiation, invasiveness of the cancer cells, angiogenesis andapoptosis.

According to yet another embodiment, the therapeutic agent is acytotoxic compound selected from, but not restricted to, agentsinhibitory of DNA synthesis and function selected from the groupconsisting of: adriamycin, bleomycin, chlorambucil, cisplatin,daunomycin, ifosfamide and melphalan; agents inhibitory of microtubule(mitotic spindle) formation and function: vinblastine, vincristine,vinorelbine, paclitaxel (taxol) and docetaxel; anti metabolites:cytarabine, fluorouracil, fluoroximidine, mercaptopurine, methotorexate,gemcitabin and thioquanine; alkylating agents: mechlorethamine,chlorambucil, cyclophosphamide, melphalan and methotrexate; antibiotics:bleomycin and mitomycin; nitrosoureas: carmustine (BCNU) and lomustine;inorganic ions: carboplatin, oxaloplatin; interferon and asparaginase;hormones: tamoxifen, leuprolide, flutamide and megestrol acetate.

According to yet another embodiment, the therapeutic agent is ananti-tumor agent, including, but not limited to, daunomycin.

According to some embodiments, the damage caused by the therapeuticagent to the plurality of multicellular compositions is assed withreference to a plurality of untreated multicellular compositions andwith reference to the plurality of multicellular compositions beforetreatment with the therapeutic agent.

The multicellular compositions may be maintained and treated with thetherapeutic agent in vitro and in vivo. In the latter, the treatment maybe administered locally or administered systemically, for example, byintravenous injection.

2. Other Applications

Having established the feasibility of the experimental platform, a broadarray of applications to cancer research can be undertaken, ranging fromvery basic cell biological studies of biochemical and signalinginteractions between different types of tumors and surrounding humandifferentiated cells to pre-clinical testing of anti-cancer agentstargeted to disable the human neo-angiogenic response. Among others,such applications include:

Genetic manipulation of cytokine, growth factor, and enzyme systems inthe tumor cells, or in the human embryonic stem cells from which thedifferentiated microenvironments are derived. In previous tumorxenograft studies, such genetic manipulations have been carried out bytransgenic modulation of the host mouse (Huang et al., 2002) rather thanwithin differentiated human cells.

Extrapolation to human tumor cells freshly harvested from clinicalsamples.

Fractionation from within the bulk tumor population of specificsubpopulations of cells with characteristic gene expression profiles orsurface markers associated with tumorigenic properties of interest.

Pre-clinical testing of anti-angiogenic, immunotargeting or othertherapeutic anti-cancer agents and drugs whose properties might bedifferent within the context of a human differentiated cellularmicroenvironment.

Numerous additional applications can be considered for the multicellularsystems of the present invention. Among others, these includequantitation of tumor proliferation following in vivo pulse labelingwith BrdU, comparative quantitation of angiogenic responses, andcomparison of properties related to local microenvironment amongdifferent human tumor cell types, including tumor cells harvested fromclinical primary samples.

The multicellular composition of the present invention in a suitablehost animal may be further utilized for exploring aspects related to theinteraction between the cancer cells the immune systems such as:

-   -   1. Therapeutic anticancer effects of the immune system.    -   2. The influence of the normal microenvironment which surrounds        the cancer cells on the efficacy of the therapeutic activity of        the immune system.    -   3. Interactions between cells of the immune system cells and        cancer cells, for example, infiltration of T cells into tumors.    -   4. The influence of immunological factors such as cytokines and        chemokines on the migration of tumor-specific T cells and their        activity.

The following examples are to be construed in a non-limitative fashionand are intended merely to be illustrative of the principles of theinvention disclosed.

EXAMPLES Materials and Methods

Cell Culture.

The human undifferentiated embryonic stem cell clone H9.1(Itskovitz-Eldor et al. Mol. Med. 6, 88-95, 2000) were grown onmitomycin C treated mouse embryonic fibroblasts (MEF) feeder layer aspreviously described (Tzukerman et al. Mol Biol Cell 11, 4381-91, 2000).The HEY cell line that was initiated from a disaggregated xenograftovarian tumor (Braunstein et al., Cancer Res. 61, 5529-36 2001) wasgrown in RPMI 1640 supplemented with 10% FCS and 1% L-glutamine(Biological Industries, Israel).

Reporter Plasmid and Stable Transfection.

The cDNA coding region for the green fluorescence protein (OFP) fuseddownstream to the histone H2A (Zur et al., EMBO J. 21, 4500-10, 2002)was inserted into AgeI and NotI restriction sites of the pEGFP-N1expression vector (Clontech). Stable transfection of HEY cells wascarried out using FuGENE6™ reagent (Roche) and 300 g/ml G418 (LifeTechnologies™) for selection of stable clones.

Teratoma Formation.

Undifferentiated hES cells were harvested using 1 mg/ml collagenase typeIV (Life Technologies™) and injected into the hindlimb of SCID/beigemice (˜5×10⁶ cells per injection). Teratomas were palpable after 4weeks. At 61 days following initial injection of H9.1 cells, 10⁶ HEY-GFPcells were injected into the teratoma and permitted to grow for anadditional 21 days. Control non-injected teratomas, HEY-GFP injectedteratomas, as well as tumor nodules derived from direct injection ofHEY-GFP, were all harvested at 82 days.

Histological Analysis.

Teratomas were harvested, fixed for 48 h in 10% neutral bufferedformalin, transferred into 70% ethanol and processed using a routine waxembedding procedure for histologic examination. 6-μm paraffin sectionswere mounted on Super FrostPlus® microscope slides (Menzel-Glaser,Germany) and stained with hematoxylin/cosin.

Immunohistochemistry.

Sides were deparaffnized using xylene and rehydrated through a series ofgradients of alcohol to water. Antigens were retrieved using microwaveexposure at 90° C. for 8 minutes in a citrate buffer pH6.1. Endogenousperoxidase enzyme activity was blocked using 3% hydrogen peroxidase inmethanol for 30 minutes at room temperature. Slides were washed indistilled water and in PBS pH7.4 and then were blocked using 10%non-immuned goat serum (GFP—for 1 hour, CD31 and CD34—for 24 hours at 4°C.). Slides were incubated for 24 hours at 4° C. with the primaryantibodies: rabbit polyclonal anti GFP-1:2000 (Molecular Probes), mousemonoclonal anti human CD34-1:50 (DAKO), rabbit polyclonal anti mouseCD31 1:2000, followed by incubation with goat anti-rabbit or anti-mousebiotinylated secondary antibody. Pre-immune rabbit or mouse sera wereused as negative controls. Detection was accomplished usingHistostain-SP (AEC) kit (Zymed Lab). Counterstaining was carried outusing hematoxylin.

Example 1 In Vitro Culture of Pluripotent Human Embryonic Stem Cells

Large stocks of primary MEFs were prepared as described by Robertson(Robertson E. G. Ed., Teratocarcinomas and embryonic stem cells: apractical approach in Practical approach series, IRL Press 1987, 71-112)and stored in liquid nitrogen. After each thaw, cells were used for only3-5 passages. The human ES-H9 cells were maintained in theundifferentiated state by propagation in culture on a feeder layer ofMEFs that was mitotically inactivated by gamma irradiation with 35 Gyand plated on gelatin-coated six-well plates.

Cells were grown in knockout Dulbecco's modified Eagle's medium (Gibco,Grand Island, N.Y.) supplemented with 20% serum replacement (Gibco), 1%nonessential amino acids (Gibco), 0.1 mM 2-mercaptoethanol (Gibco), 1 mMglutamine (Biological Industries, Bet-Haemek, Israel), 4 ng/ml humanbFGF (PeproTech, Rocky Hill, N.J.). Cells were cultured in 5% CO₂, 95%humidity and were routinely passaged every 4-5 days after disaggregationwith 0.1% collagenase IV (Gibco).

Methods for the induction of induction of hES differentiation wereapplied (e.g. Keller in Curr. Op. Cell Biol. 7:862, 1995). About 10⁷undifferentiated hES cells were disaggregated and cultured in suspensionin 100-mm bacterial-grade petri dishes (Greiner, Frickenhausen,Germany), which resulted in induction of synchronous differentiationcharacterized by initial formation of small aggregates and followed bythe acquisition of the configuration of embryoid bodies.

Alternatively, hES colonies were left unpassaged until confluence (10days) and were replated on gelatinized six-well tissue culture plates inthe absence of a feeder layer. The cells spontaneously differentiated toan array of cell phenotypes. The growth media used in differentiationwere as described above.

Example 2 Development of Human Cancer Cells within Teratomas

To determine whether human cancer cells injected into mature andwell-developed teratomas growing in immunocompromised mice, would growwithin the teratoma and whether they would display properties associatedwith malignancy such as invasiveness and recruitment of blood vesselsfrom the teratoma HEY-ovarian cancer cells (Buick et al., Cancer Res.45, 3668-76, 1985) were used. These cells have been stably transfectedso as to constitutively express a nuclear histone H2A-green fluorescentreporter fusion protein (HEY-GFP), which enables to track them withinthe surrounding microenvironment of normal differentiated human cellsand tissue.

Eighty-two days after the intramuscular injection of undifferentiatedhuman embryonic stem cells (H-9.1 clone) into the hindlimb musculatureof SCID/beige mice, typical nodules appeared and increased in sizeprogressively as has been previously described (Amit et al., ibid).Stained sections of such nodules reveal them to be teratomas, containingnumerous and varied complex differentiated structures as has beenpreviously reported (Thomson et al, Science 282, 1145-7, 1998).Injection of 10⁶ HEY-GFP cells at day 61 into such teratomas inSCID/beige mice (FIG. 1) yielded a different gross morphologicappearance compared to the direct hindlimb intramuscular injection of anequal aliquot of HEY-GFP cells. In the case of direct intramuscularinjection of tumor cells, the well-described appearance of small nodulesat each injection site was observed, in which there was poor demarcationof the nodule from the surrounding murine muscle tissue, and a markedlyhemorrhagic surface. In contrast, following injection of an equalaliquot of cells at day 61 into the teratoma, the teratoma surfaceappeared well circumscribed with relatively few blood vessels andabsence of hemorrhage. HEY-GFP cells were injected into the teratomasand stained sections with Gomori technique for reticulin fibers (Gomori,Am. J. Path. 13, 993, 1937) was utilized to detect the histochemicalappearance of the mixed teratoma structures obtained 21 days afterinjection of HEY-GFP cells into these teratomas. Histologic appearanceat lower power magnification revealed these mixed structures to becomprised of regions with the typical appearance of teratomas derivedfrom human embryonic stem cells with a variety of mature differentiatedstructures (FIG. 2A), regions of tumor cells with the appearance of ahomogeneous mass of cells with the characteristic morphology ofadenocarcinoma (FIG. 2B) and also exhibiting high proliferative capacityas exhibited by the number of cells in mitosis and by PCNA staining(data not shown), as well as boundary regions in which tumor cellsappeared adjacent to differentiated teratoma structures such as theneurovascular bundle shown in FIG. 2C.

Example 3 Tumor Cell Invasion into Normal Tissue

Since invasiveness is a hallmark characteristic of tumorigenesis, andbecause of the appearance of tumor cells adjacent to human ES derivedteratoma structures, we sought to track the possible migration andinfiltration of tumor cells into normal differentiated tissue. For thispurpose, since the HEY-GFP cells are stably transfected toconstitutively express GFP, it was possible to track HEY-GFP cellinfiltration using immunohistochemistry for GFP. FIG. 3A shows nuclearGFP positive immunohistochemical staining in a field of tumor cells.Although there is variable intensity of staining, positive staining iseasily detectable in tumor cell nuclei. FIGS. 3B-C show GFP positivecells, which have invaded and interspersed among teratoma-deriveddifferentiated cells and structures such as adipocytes and migrated tothe other side of a neural structure. HEY-GFP positive cells alsomigrated to surrounding connective tissue (not shown). In the case ofnodules generated by direct intramuscular injection of HEY-GFP ovariancancer cells in SCID/beige mice, there is the expected invasion of GFPpositive cells into the surrounding murine muscle tissue (not shown).

Example 4 Tumor Induced Angiogenesis in Teratoma Host Tissue

Growth of tumor-derived nodules in immunocompromised mouse models, hasbeen extensively used to demonstrate tumor angiogenesis, which isconsidered crucial for tumor growth. Blood vessels of murine origin havebeen shown to grow within the tumor nodules, and anti-angiogenic agentshave been shown to disrupt this effect and induce tumor regression insuch experimental models.

In order to determine whether tumors growing within hES-derivedteratomas would elicit the growth of teratoma-derived blood vessels ofhuman origin adjacent to and within the tumor endothelial markerantibodies were used. Specific markers were used for mouse and for humanblood vessels, i.e. the CD34 and CD31 human and mouse specific surfaceendothelial marker antibodies respectively, enabling to distinguishbetween these two types of blood vessels.

FIG. 4A shows a positive control of immunostaining with human specificCD34 antibody of blood vessels in a specimen of human breast carcinoma.FIGS. 4B and C are photomicrographs showing low- and higher-powermagnifications of CD34 positive immunostaining of an arteriole adjacentto a mass of HEY tumor cells growing within a human teratoma.Specificity of staining of the endothelial cell layer is evident in thehigher power magnification. FIGS. 4D-F show a variety of additionalhuman CD34 positively staining blood vessels of various sizes andconfiguration (arteriole, venule, capillary and immature small bloodvessel characteristic of tumor-induced angiogenesis), adjacent to andwithin tumor cells. Hepatic sinusoid endothelium immunostained by mousespecific CD31 antibody is shown in normal mouse liver tissue (FIG. 5A),and in a HEY-derived tumor nodule following direct intramuscularinjection in SCID/beige mice (FIG. 5B). In contrast, mouse-specific CD31immunostaining is not evident in HEY ovarian cancer-derived cellsgrowing within an hES teratoma, despite the presence of blood vesselsadjacent to and within the tumor mass (FIG. 5C).

Thus, human ovarian cancer cells elicit a neo-angiogenic response, whichis of murine origin in the case of tumors growing directly within thesurrounding murine tissue, and of human origin in the case of growthwithin normal differentiated human tissue of embryonic stem cell origin.Other blood vessels within the teratoma tissue itself were stainedeither with CD31 or with CD34 reflecting neo-angiogenesis of murineorigin at early stages of teratoma generation in the mouse andsubsequent differentiation of human ES cells into blood vessels of humancellular origin, and did not differ in appearance between control versustumor-injected teratomas.

Example 5 Multicellular Compositions Comprising Non-Ovarian Cancer CellLines

In order to demonstrate that the experimental model is applicable to awide variety of tumor cell lineages, we have modified several tumor celllines so as to constitutively express GFP-H2A driven by the CMVpromoter. Among these cell lines are A431 (cervical squamous epidermoidcarcinoma), PC3 and LNCap1740 (prostate carcinoma cell lines).

These cell lines were shown to generate nodules in SCID/beige mice. TheA431 cell line was also injected into hES derived teratomas and we havealready demonstrated tumor generation within the human cellularmicroenvironment. The A431 tumor line is characterized by a very highdegree of neoangiognesis and will be used also in specific aim 1.4 andin experiments involving anti angiogenic factors in specific aim 2.2.

In addition specific antibodies will be used in these teratomas toidentify tumor cells as follow: A431 tumor cells will be detected usinganti-EGF receptor antibody, which is highly expressed in these cells.Prostate-specific membrane antigen (PSA) will be used in teratomascontaining tumors derived from injection of prostate carcinoma celllines.

We have injected 2×10⁶ A431 cells (epidermoid carcinoma cell line),3×10⁶ PC3 cells (prostate cancer cell line) and 3×10⁶ LNCap cells(prostate cancer cell line) into established teratomas that weredeveloped IM in SCID/beige mice following injection of hES cells. Allthree cancer cell lines stably express a fusion protein comprised ofenhanced green fluorescence protein EGFP and hisone H2A that isexpressed in the cell nuclei.

Teratomas bearing A431 cells were harvested 10 days following injectionof cancer cells. Teratomas bearing PC3 and LNCap cells were harvested 37days following injection. Paraffin sections of harvested teratomasstained with hematoxylin/eosin reveal a homogenous mass of tumor cellswithin the characteristic differentiated structures of the teratomas.Within the mass of tumor cells a high number of cells in mitosis and alarge amount of small blood vessels can be observed. More establishedblood vessels could be observed at the boundary regions between thetumor and the teratomas. Tumor cells were identified usingimmunohistochemistry (IHC) with anti GFP antibody.

Tumors derived from injection of A431 cells that express high levels ofEGFR exhibited overlapping staining of tumor cells with anti GFPantibody and anti EGFR antibody.

Tumors derived from injection of PC3 cells or LNCap cells that expresshigh levels of PSA (prostate specific antigen) exhibited overlappingstaining of tumor cells with anti GFP antibody and anti PSA antibody.

In the case of A431, invasion and migration of tumor cells into theteratoma tissue and generation of new nodules as a result of thismigration in the teratomas tissue are highly observed following stainingwith anti GFP and anti EGFR antibodies.

As mentioned above A431 tumor line is characterized by a very highdegree of neoangiogenesis. To distinguish mouse-derived fromhuman-derived blood vessels, we performed IHC using human-specific VonWilebrant Factor (vWF), α-Smooth Muscle Actin, CD34 and mouse specificCD31 antibodies. Blood vessels of human origin (teratomas derived) wereobserved within the teratoma and adjacent to the tumor. Immature smallblood vessels of human origin were observed within the tumorcharacteristic of tumor-induced neoangiogenesis.

The results confirm that the multicellular compositions of the presentinvention may comprise any cancer cell lineage.

Example 6 Effect of Anti-Cancer Therapies on a Multicellular CompositionComprising Non-Ovarian Cancer Cell Lines

The utility of the multicellular compositions of the invention fortesting anti-cancer agents and treatments was demonstrated using arecombinant immunotoxin antibody that reacts with the Lewis^(Y)(Le^(Y)), a well characterized antigen that is highly expressed in manycarcinomas. This anti-cancer immunotherapy was shown to exhibit acomplete regression of A431 tumors in mice (Reiter Y, 1998, TrendsBiotechnol. 16:513-20).

The experimental set up had 6 different groups each containing 5SCID/beige mice. 5×10⁶ hES cells were injected into the hind limb andteratomas were allowed to develop for 7 weeks. 2×10⁶ A431 cells wereinjected into the teratomas and allowed to develop into a tumor withinthe teratomas for 5 days before applying immunotherapy. The differentgroups were treated as follows:

1. Mice bearing teratomas only.

2. Mice bearing tumor containing teratomas.

3. Mice bearing tumor containing teratomas treated with immunotoxin; 2μg/1001 injected into the tail vein 3 times, every other day.

4. Mice bearing teratomas treated with immunotoxin, 2 μg/100 μl,injected into the tail vein 3 times, every other day.

5. Mice bearing teratomas treated with PBS.

6. Mice bearing tumor containing teratomas treated with PBS.

For comparison (control), A431 cells were injected directly into thehind limb of SCID/beige mice, and received the same treatments as theteratomas.

Two days following the last treatment, all mice were sacrificed,teratomas were harvested and subjected to routine wax embeddingprocedure for histological examination. Six micrometer paraffin sectionswere stained with hematoxylin/eosin or subjected to IHC using anti GFPand anti EGFR to detect tumor cells within the teratomas.

Direct injection of A431 cells into the mouse hind-limb resulted indevelopment of control tumors which exhibited a high degree ofangiogenesis. Tumor cells were GFP and EGFR positive usingImmunohistochemistry (IHC). Blood vessels within the tumor werepositively stained for mouse specific CD31 antibody, and negative forhuman specific vWF, α-Smooth Muscle Actin and CD34 antibodies. Injectionof immunotoxin trough the tail vein resulted in complete regression asobserved by palpation. Histological examinations revealed a smallremnant of unviable tumor cells with small and condensed nuclei thatwere negatively stained for EGFR.

Histologic appearance of tumor bearing teratomas without treatment andtumor bearing teratomas treated with PBS, revealed that the tumor cellsdeveloped into a homogenous mass of cells with characteristic morphologyof abnormal carcinoma. Tumor cells exhibited high proliferative capacityat tumors periphery. Tumor cells that invaded into the normalsurrounding microenvironment were also detected, as indicated by GFP andEGFR positive cells interspersed among teratomas derived connectivetissue, adipocytes, lamina propria tissue and neurovascular bundles. Newfoci of viable tumor cells were also observed.

Upon immunotherapy a complete regression of tumor growth within theteratomas was demonstrated. However small foci (100 μm-600 μm) of viabletumor cells, were observed suggesting that a longer immunotherapytreatment and/or addition of another treatment (e.g. withanti-angiogenic factors) would completely eliminate tumor cells from theteratomas.

IHC of sections derived from teratomas bearing tumors, in the presenceor absence of immunotoxin treatment, stained with human specific vWF,α-Smooth Muscle Actin and CD34 antibodies revealed the existence ofestablished and immature small blood capillaries of human origin withinthe multicellular complex of teratomas and the cancer cells.

Example 7 Magnetic Resonance Imaging (MRI) Analysis of MulticellularCompositions In Vivo

The following models were incorporated in the MRI experiments:

Mice bearing tumors;

Mice bearing teratomas; and

Mice bearing tumor within a teratoma.

Tumor tissue appeared homogenous compared to the teratomas tissue due tothe existence of different differentiated structures. MRI analysis alsoindicated that the tumors which developed directly in the hind-limb ofthe mice exhibits a higher degree of angiogenesis as compared to tumorsdeveloped within a teratoma.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without undue experimentation and withoutdeparting from the generic concept, and, therefore, such adaptations andmodifications should and are intended to be comprehended within themeaning and range of equivalents of the disclosed embodiments. It is tobe understood that the phraseology or terminology employed herein is forthe purpose of description and not of limitation. The means, materials,and steps for carrying out various disclosed functions may take avariety of alternative forms without departing from the scope of theinvention.

1. A method of screening therapeutic agents using a multicellularcomposition comprising human cancer cells within and surrounded by amicroenvironment of non-malignant human cells selected from pluripotenthuman embryonic stem cells and non-malignant human tissue derived fromdifferentiated human embryonic stem cells and wherein the cancer cellsmaintain their abnormal phenotype, the method comprising contacting themulticellular composition with at least one candidate therapeutic agent,and determining the effect of the at least one therapeutic agent on themulticellular composition.
 2. The method according to claim 1,comprising: (a) culturing human embryonic stem cells in conditions whichpromote generation of embryoid bodies; (b) determining the formation ofat least one embryoid body in the culture of (a); (c) injecting cancercells into the at least one embryoid body thereby obtaining at least onemulticellular composition; optionally, (d) determining the presence ofcancer cells within said at least one multicellular composition; (e)contacting said at least one multicellular composition obtained in (d)to a therapeutic agent; and (f) determining the effect of thetherapeutic agent on said at least one multicellular composition.
 3. Themethod according to claim 1, wherein determining the effect of thetherapeutic agent on said at least one multicellular compositioncomprises evaluating one or more parameters selected from the groupconsisting of: cell proliferation, cell differentiation, invasiveness ofthe cancer cells, angiogenesis and apoptosis.
 4. The method according toclaim 1, comprising: (a) injecting undifferentiated human embryonic stemcells into a host animal; (b) determining the formation of at least oneteratoma in the host animal; (c) injecting cancer cells into the atleast one teratoma thereby obtaining at least one multicellularcomposition; (d) determining the presence of cancer cells within the atleast one multicellular composition; (e) treating the host animal havingsaid at least one multicellular composition obtained in (d) with atherapeutic agent; and (f) determining the effect of the therapeuticagent on said at least one multicellular composition.
 5. The method ofclaim 1, comprising: (a) culturing undifferentiated human embryonic stemcells in conditions which promote generation of embryoid bodies; (b)determining the formation of at least one embryoid body in the cultureof (a); (c) injecting cancer cells into the at least one embryoid bodythereby obtaining at least one multicellular composition; optionally,(d) determining the presence of cancer cells within said at least onemulticellular composition; (e) implanting said at least onemulticellular composition into a host animal; optionally, (f) treatingthe host animal with a composition comprising a therapeutic agent; and(g) determining the effect of therapeutic agent on said at least onemulticellular composition.
 6. The method of claim 5, wherein step (e)further comprises occluding said at least one multicellular compositionwithin a barrier membrane prior to implanting said at least onemulticellular composition in a host animal.
 7. The method of claim 5,wherein said at least one multicellular composition is injected into asite in the host animal selected from the peritoneal cavity and apredefined locus.
 8. The method of claim 4, wherein treating the hostanimal is performed by topical administration of said therapeutic agentto said at least one multicellular composition.
 9. The method of claim4, wherein the host animal is immunodefficient.
 10. The method of claim1, wherein the therapeutic agent is selected from the group consistingof: a cytotoxic compound, a cytostatic compound, anticancer drug, anantisense compound, an anti-viral agent, an agent inhibitory of DNAsynthesis and function and an immunotherapeutic agent.
 11. The method ofclaim 10, wherein the at least one therapeutic agent is conjugated to anagent selected from the group consisting of: a fluorescent marker,chemiluminescent marker, imaging agent and a carrier.
 12. The method ofclaim 11, wherein the imaging agent is selected from the groupconsisting of: gadolinium, yttrium, lutetium and gallium; radioactivemoieties, such as, radioactive indium, rhenium and technetium,fluorescein isothiocyanate (FITC), green fluorescent protein (GFP), cyanfluorescent protein (CFP), rhodamine I, II, III and IV, rhodamine B, androsamine.
 13. The method of claim 10, wherein the immunotherapeuticagent is of human origin.
 14. The method of claim 10, wherein theimmunotherapeutic agent is selected from the group consisting of: anantibody or any active fragment thereof, a cytokine, a chemokine, apolynucleotide encoding same and a cell of the immune system.
 15. Themethod of claim 10, wherein the therapeutic agent comprises at least oneoligonucleotide, selected from the group consisting of: antisense, sensenucleotide sequence, short interfering RNA, ribozyme and aptamer.
 16. Amethod for evaluating treatment efficacy of a therapeutic agent,comprising assessing the effect of the therapeutic agent on cancer cellswithin and surrounded by a microenvironment of non-malignant human cellsselected from pluripotent human embryonic stem cells and non-malignanthuman tissue derived from differentiated human embryonic stem cells;wherein the cancer cells maintain their abnormal phenotype.
 17. Themethod of claim 16, comprising contacting a plurality of multicellularcompositions with a therapeutic agent and assessing the damage caused bythe therapeutic agent to the non-malignant human cells.
 18. The methodof claim 16, comprising contacting a plurality of multicellularcompositions with a therapeutic agent and assessing the damage caused bythe therapeutic agent to the cancer cells.
 19. The method of claim 17,wherein the damaged caused by the therapeutic agent is assessed byevaluating at least one of the parameters selected from the groupconsisting of: cell proliferation, cell differentiation, invasiveness ofthe cancer cells, angiogenesis and apoptosis.
 20. The method of claim16, wherein the therapeutic agent is selected from the group consistingof: a cytotoxic compound, a cytostatic compound, anticancer drug, anantisense compound, an anti-viral agent, an agent inhibitory of DNAsynthesis, an agent inhibitory for DNA function and an immunotherapeuticagent.
 21. The method of claim 20, wherein the therapeutic agent isselected from the group consisting of: adriamycin, bleomycin,chlorambucil, cisplatin, daunomycin, ifosfamide and melphalan; agentsinhibitory of microtubule (mitotic spindle) formation and function:vinblastine, vincristine, vinorelbine, paclitaxel (taxol) and docetaxel;anti metabolites: cytarabine, fluorouracil, fluoroximidine,mercaptopurine, methotrexate, gemcitabin and thioquanine; alkylatingagents: mechlorethamine, chlorambucil, cyclophosphamide, melphalan andmethotrexate; antibiotics: bleomycin and mitomycin; nitrosoureas:carmustine (BCNU) and lomustine; inorganic ions: carboplatin,oxaloplatin; interferon and asparaginase; hormones: tamoxifen,leuprolide, flutamide, daunomycin and megestrol acetate.